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Carbon nanostructures-silica aerogel composites were synthesized and characterized to assess the effect of carbon nanotubes (CNTs) or graphene oxide (GO) on the silica aerogel properties. The sol-gel chemistry was based on methyltrimethoxysilane (MTMS) and 3-aminopropyltrimethoxysilane (APTMS) as silica precursor system, with varying amounts of APTMS (0–20% mol of Si). APTMS significantly impacted the materials' physical properties. The chemistry and microstructure were investigated by FTIR, NMR, TEM, SEM, SAXS and BET. The addition of CNTs induced the growth of the silica matrix around them; thus, an elongated shape was observed in the silica structural units. APTMS and CNTs have a synergistic effect on the mechanical properties, increasing the Young's modulus up to 14 MPa. Small amounts of carbon materials (∼1 wt%) in the MTMS-matrix improved its thermal insulation property, particularly for temperatures above 50 °C. In terms of electrochemical properties, the carbon nanostructures lead to higher specific capacitances and a reduction in resistance. The characterizations here performed allowed a better understanding of the interactions between the silica and carbon phases. The possibility to obtain materials with tailored properties demonstrates their application potential in several areas, such as thermal insulation and energy storage.

Biopolymer aerogels are an emerging class of materials with potential applications in drug delivery, thermal insulation, separation, and filtration. Chitosan is of particular interest as a sustainable, biocompatible, and abundant raw material. Here, we present urea-modified chitosan aerogels with a high surface area and excellent thermal and mechanical properties. The irreversible gelation of an acidic chitosan solution is triggered by the thermal decomposition of urea at 80 °C through an increase in pH and, more importantly, the formation of abundant ureido terminal groups. The hydrogels are dried using either supercritical CO2 drying (SCD) or ambient pressure drying (APD) methods to elucidate the influence of the drying process on the final aerogel properties. The hydrogels are exchanged into ethanol prior to SCD, and into ethanol and then heptane prior to APD. The surface chemistry and microstructure are monitored by solid-state NMR and Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen sorption. Surprisingly, large monolithic aerogel plates (70 × 70 mm2) can be produced by APD, albeit at a somewhat higher density (0.17-0.42 g/cm3). The as prepared aerogels have thermal conductivities of ∼24 and ∼31 mW/(m·K) and surface areas of 160-170 and 85-230 m2/g, for SCD and APD, respectively. For a primarily biopolymer-based material, these aerogels are exceptionally stable at elevated temperature (TGA) and char and self-extinguish after direct flame exposure. The urea-modified chitosan aerogels display superior mechanical properties compared to traditional silica aerogels, with no brittle rupture up to at least 80% strain, and depending on the chitosan concentration, relatively high E-moduli (1.0-11.6 MPa), and stress at 80% strain values (σ80 of 3.5-17.9 MPa). Remarkably, the aerogel monoliths can be shaped and machined with standard tools, for example, drilling and sawing. This first demonstration to produce monolithic and machinable, mesoporous aerogels from bio-sourced, renewable, and nontoxic precursors, combined with the potential for reduced production cost by means of simple APD, opens up new opportunities for biopolymer aerogel applications and marks an important step toward commercialization of biopolymer aerogels.

Aerogels are mesoporous materials with a rapidly growing thermal insulation market interest, partly because ambient pressure drying (APD) reduces cost. Silica gels must be hydrophobized to prevent condensation reactions and irreversible shrinkage during APD. Here, we study how hydrophobization with mono-, di-, and trifunctional organoalkoxysilanes (M, D, T) and their mixtures, affects spring-back, density, surface area, pore size and hydrophobicity. All aerogels were synthesized from a polyethoxydisiloxane precursor prepared from a tetraalkoxysilane (tetraethoxysilane, TEOS). Aged gels, hydrophobized with trimethylethoxysilane (M100), display the highest spring-back and lowest density (0.100 g/cm3) upon APD drying. Hydrophobization with pure dimethyldiethoxysilane (D100) or methyltriethoxysilane (T100) leads to excessive shrinkage and respective densities of 0.440 and 1.450 g/cm3 due to the self-polymerization from the di- and trifunctional silanes: in the D100 material, the formation of polydimethyldisiloxane (PDMS) is evident in the 29Si NMR spectra, whereas 3D silica structures (beads) are apparent for the T100 sample. Aerogels hydrophobized with binary and ternary mixtures of M, D and T display systematic variations in density: nearly constant (

Tannin-silica hybrid materials are expected to feature excellent mechanic-chemical stability, large surface areas, high porosity and possess, after carbothermal reduction, high thermal stability as well as high thermal conductivity. Typically, a commercially available tetraethoxysilane is used, but in this study, a more sustainable route was developed by using a glycol-based silica precursor, tetrakis(2-hydroxyethyl)orthosilicate (EGMS), which is highly water-soluble. In order to produce highly porous, homogeneous hybrid tannin-silica aerogels in a one-pot approach, a suitable crosslinker has to be used. It was found that an aldehyde-functionalized silane (triethoxysilylbutyraldehyde) enables the covalent bonding of tannin and silica. Solely by altering the processing parameters, distinctly different tannin-silica hybrid material properties could be achieved. In particular, the amount of crosslinker is a significant factor with respect to altering the materials’ properties, e.g., the specific surface area. Notably, 5 wt% of crosslinker presents an optimal percentage to obtain a sustainable tannin-silica hybrid system with high specific surface areas of roughly 800–900 m2 g−1 as well as a high mesopore volume. The synthesized tannin-silica hybrid aerogels permit the usage as green precursor for silicon carbide materials.

Available data suggests that granulated aerogels can be of interest in terms of their sound absorption performance in the audio frequency range. However, there is still no thorough understanding of the complex physical phenomena which are responsible for their observed acoustical properties. This work is an attempt to address this gap through advanced material characterization methods and mathematical modelling. Aerogel samples are produced through a two-step, acid-base sol-gel process, with sol silica concentration and density being the main variables. Their pore structure is carefully characterized by nitrogen sorption analysis and scanning electron microscopy. The acoustical properties of hard-backed granular silica aerogels are measured in an impedance tube and the results predicted accurately with the adopted theoretical model. Although silica aerogels have over 90% of open interconnected pores, this was neither reflected in the measured acoustical properties nor the parameter values predicted with the model. Novel results show that only a proportion of the micro and mesopores in the direct vicinity of the grain surface influenced the acoustical properties of aerogels. Further work in the hierarchical pore structure of aerogels is required to better understand the roles of different pore scales on the measured acoustical properties of a granulated aerogel.

Silica aerogels are highly porous (~95%), predominantly mesoporous (20–50 nm) materials with very high surface area (~800 m2/g), but applications that valorize the chemical properties linked to the high surface area lag behind those that valorize the pore structure (thermal insulation). Here, we present widely applicable protocols to synthesize and characterize organo-functionalized silica aerogels with high surface area (356–1177 m2/g) and high mass loadings of surface functional groups (1.0–4.9 mmol/g, 0.9–3.9 molecules/nm2). Wet silica gels are soaked into dilute solutions containing pre-hydrolyzed organofunctional trialkoxysilanes, followed by supercritical CO2 drying. The retention of the various functional groups in the dry aerogels is confirmed by FTIR and their concentrations quantified by solid-state NMR spectroscopy. The mild reaction conditions are compatible with all tested functional groups (silanol, ethoxy, trimethylsilyl, amino, vinyl, methyl methacrylate, epoxy, phosphonate), without the need to optimize for each specific functional silane, making the synthesis of organofunctionalized aerogels a routine task.

Supercritical drying is widely considered as the gold standard to produce aerogels that preserve the microstructure of the gels, but we have found this is not always the case. Chitosan aerogel, one of the emerging biopolymer aerogels, was prepared by chemical cross-linking gelation, followed by solvent exchange with methanol and supercritical drying using CO2. Small-angle X-ray scattering analysis shows that the structure of the wet gel, which consists of Gaussian chains of individual molecular strands, converts into a nanofibrous network during CO2 processing. In situ observation reveals a drastic shrinkage of the gel in CO2, demonstrating that physical coagulation caused by the low affinity between chitosan and CO2 is the main structure-forming step. These results challenge the common perception of supercritical drying: it is no longer an inactive drying method, but rather an active nanostructure forming a tool to produce porous biopolymer materials with tailored structure and properties.

Aldehyde-free, transparent chitosan aerogel is reported. The aerogel was prepared by thermal decomposition of urea to induce gelation of a chitosan solution, followed by solvent exchange to ethanol, and supercritical drying. Low urea concentrations (≤ 25 g L-1) result in transparent and highly mesoporous aerogels, while higher urea concentrations (≥ 30 g L-1) produce opaque, more macroporous aerogels. The high surface areas of > 400 m2 g-1, large mesopore volumes up to 3.5 cm3 g-1, and optical transparency of the low-urea aerogels indicate a high structural homogeneity at the mesoscale, and the properties comparable to previously reported transparent chitosan aerogels prepared with formaldehyde crosslinking. The macroscopic size changes of the wet gels indicate that microstructure formation is controlled by the timing of chitosan coagulation, which depends among others on urea concentration. The aldehyde-free, microstructure-tunable process provides a new series of transparent biopolymer aerogels with "true aerogel" mesoporous structures.

Chitosan is an abundant biopolymer derived from food waste with attractive properties, particularly its high biocompatibility and easy chemical processability. Here, we review the rapidly expanding literature on chitosan-based porous materials with a focus on the gelation mechanisms, the three-dimensional multiscale structural control, and the diverse chemical functionality not accessible by other biopolymers. The properties vary widely: from supercritically dried, mesoporous chitosan aerogels to very light, freeze-dried macroporous scaffolds. Porous chitosan displays impressive performance at the laboratory scale, but the highly (meso)porous nature amplifies not only the beneficial functionality of chitosan, but also its drawbacks, resulting in serious barriers to industrialization. In order to facilitate technology transfer, we critically discuss the practical feasibility of chitosan aerogels in potential applications compared to conventional and other biopolymer-based porous or nonporous materials.

Freeze-dried nanofibrous scaffolds are flexible, but typically have high thermal conductivities. Conversely, silica aerogel has an ultra-low thermal conductivity, but is brittle. Here, the impregnation of pullulan/PVA nanofiber scaffolds with hydrophobic silica aerogel decreased the thermal conductivity from 31.4 to 17.7 mW/(m·K). The compatibility between the silylated nanofibers and the silica aerogel promotes the overgrowth of silica particles onto the fiber surfaces and the fiber incorporation. The composites display improved compressive and tensile properties compared to the neat pullulan scaffold and silica aerogel. The composite's E-modulus is 234 kPa compared to 4 kPa for the pullulan scaffold and 102 kPa for the silica aerogel. The composite's tensile strength is five times higher than that of the silica aerogel. Because of its reduced brittleness, the pullulan-silica aerogel composites can be shaped using a sharp blade. The composites can sustain uniaxial compression up to 80% strain, but the decompressed composites display two times higher densities because the strain is partially irreversible. This densification reduces thermal conductivity to 16.3 mW/(m·K) and increases final compressive strength by a factor of seven. Both the as prepared and densified composites demonstrate unique material properties in terms of thermal conductivity, mechanical strength and machinability. Keywords: Nanocomposite, Polysaccharide, Nanofibers, Hybrid aerogels, Densification

Polymer nanocomposites reinforced with inorganic fillers have sparked new aerospace, sports goods, automotive, and civil engineering applications. Here, epoxy nanocomposites with both hydrophobic a...

Silica aerogels have only half the thermal conductivity of conventional insulation, but their application potential is limited by the poor mechanical properties. The fragility arises from the thin necks between the silica nanoparticle building blocks. Here, we produce strong silica aerogels through co-gelation of the polyethoxydisiloxane precursor with a variety of silane terminated prepolymers that reinforce the inter-particle necks, followed by hydrophobization and supercritical CO2 drying. All prepolymers enabled the synthesis of aerogels with excellent thermal and mechanical properties, but the shortest prepolymer (∼2–3 nm long) yielded the best results. The hybrid aerogels can sustain uniaxial compression without brittle rupture to at least 80% strain for all prepolymer concentrations (5–50 wt%), leading to a final strength of up to 21 MPa, an E modulus up to 3.4 MPa, and an up to 400 times lower dust release rate. In contrast to classical reinforcement strategies, the mechanical improvement does not come with a penalty in thermal conductivity, which remains between 14 and 17 mW m−1 K−1. The hybrid aerogels are a unique class of superinsulating materials with superior thermal and mechanical properties and a scalable production process.

Silica aerogels can be hydrophobized with a variety of functional groups, resulting in different material properties. Here we compare the mobility of hydrophobic groups using neutron spectroscopy. Data were collected between 1.5 and 300 K on the MARS backscattering spectrometer at SINQ (PSI) for three different silica aerogels and octakis(trimethylsiloxy)silsesquioxane (Q8M8) as a reference. The mobility persists to below 10 K for silica aerogels whose surfaces are decorated with trimethylsilyl (TMS) and ethoxy groups. The high low-temperature mobility of the hydrogen in these surface functional groups originates from the large rotational freedom in the aerogel’s open mesopores. In contrast, the mobility freezes in below 30 K for Q8M8, consistent with a reduced rotational freedom within the dense Q8M8 crystal structure. At room temperature, both the rotations of hydrogen within the methyl groups and the rotations of the entire TMS groups contribute to the mean square displacements for both the silylated s...

Polyisocyanate based aerogels combine ultralow thermal conductivities with better mechanical properties than silica aerogel, but these properties critically depend on the nature of the gelation solvent, perhaps more so than on any other parameter. Here, we present a systematic study of the relationship between the polyurethane-polyisocyanurate (PUR–PIR) aerogel microstructure, surface area, thermal conductivity, and density and the gelation solvent’s Hansen solubility parameters for an industrially relevant PUR–PIR rigid foam formulation. We first investigated aerogels prepared in acetone-dimethyl sulfoxide (DMSO) blends and observed a minimum in thermal conductivity (λ) and maximum in specific surface area for an acetone:DMSO ratio of 85:15 v/v. We then prepared PUR–PIR aerogels in 32 different solvent blends, divided into three series with δDispersion, δPolarity, and δH-bonding fixed at 15.94, 11.30, and 7.48 MPa1/2, respectively, corresponding to the optimum parameters for the acetone:DMSO series. The ...

Understanding the behavior of halogens (Cl, Br, and I) in subduction zones is critical to constrain the recycling of trace elements and metals, and to quantify the halogen fluxes to the atmosphere via volcanic degassing. Here, the partitioning of bromine between coexisting aqueous fluids and hydrous granitic melts and its speciation in slab-derived fluids have been investigated in situ up to 840 °C and 2.2 GPa by X-ray fluorescence (SXRF) and absorption (XANES and EXAFS) spectroscopy in hydrothermal diamond-anvil cells. The partition coefficients Df/mBr range from 15.3 ± 1.0 to 2.0 ± 0.1, indicating the preferential uptake of Br by aqueous fluids at all investigated conditions. EXAFS analysis further evidences a gradual evolution of Br speciation from hydrated Br ions [Br(H2O)6]− in slab dehydration fluids to more complex structures invoving both Na ions and water molecules, [BrNax(H2O)y], in hydrous silicate melts and supercritical fluids released at greather depth (> 200 km). In dense fluids containing 60 wt % dissolved alkali-silicates and in hydrous Na2Si2O5 melts (10 wt % H2O), Br is found in a salt-like structure involving 6 nearest Na ions and several next-nearest O neighbors that are either from water molecules or the tetrahedral silicate network. Bromine (and likely chlorine and iodine) complexation with alkalis is thus an efficient mechanism for the mobilization and transport of halogens by hydrous silicate melts and supercritical fluids, which can carry high amounts of Br, up to the 1000 ppm level. Overall, our results suggest that both shallow dehydration fluids and deeper silicate-bearing fluids efficiently remove halogens from the slab in the sub-arc region, thus controling an efficient recycling of halogens in subduction zones.

Silica aerogels’ unique physical and chemical properties make them fascinating materials for a wide variety of applications. In addition to hydrophobization by silylation, aging is very important in the synthesis of silica aerogel by ambient pressure drying. Here we systematically study the effect of aging on the physico-chemical properties of silica aerogel with emphasis on ambient dried materials. Silica gels were aged for different times and at different temperatures in their gelation liquid (without solvent exchange), hydrophobized in hexamethyldisiloxane and subsequently dried either at ambient pressure or from supercritical CO2. Dynamic oscillatory rheological measurements demonstrate that aging reinforces the alcogels, particularly at high strain. The specific surface area decreases with increasing aging time and temperature as a consequence of Ostwald ripening processes during aging. With increasing aging time and temperature, the linear shrinkage and bulk density decrease and the pore size and pore volume increase for the ambient dried gels, but remain nearly constant for supercritically dried gels. Small-Angle X-ray scattering does not detect significant structural changes at length scales smaller than about hundred nanometers, but hints at systematic variations at larger length scales. The findings of this study highlight the importance of aging to increase the ability of the gel particle network to withstand irreversible pore collapse during ambient pressure drying.

A sustainable aqueous-based route is reported for the synthesis of low density mesoporous silica/chitosan nanocomposite aerogels by cogelation of a chitosan biopolymer dissolved in silicic acid. The random “cluster–cluster” aggregate silica structure intertwined at the molecular level with chitosan yields a three-dimensional semi-interpenetrating network with greatly improved mechanical properties when compared to a silica aerogel of similar density. The physical properties of the resulting aerogels depend significantly on the gelation pH. A silica aerogel reference material synthesized at a low pH of 3 features very low density and high porosity resulting in a highly elastic behavior but comparatively weak skeletal structure (final strength 80%) but with greatly increased yield strength (>7 MPa). Importantly, the rein...

Silica aerogel superinsulation products have a tremendous growth potential, particularly for industrial and pipe insulation. However, the high production cost and the poor mechanical properties prevent the adoption of silica aerogel superinsulation outside of the established niche markets. In this paper, we address these two barriers. We analyze the solvent use of current production processes for ambient-dried silica aerogel and derive a minimal solvent process that approaches the theoretical minimum of one volume of solvent for one volume of aerogel. We apply this process at the pilot scale and produce aerogel granulate with a thermal conductivity of 17.4 mW/(m·K). A review of the different mechanical reinforcement strategies reveals that strengthening typically comes with a penalty in thermal conductivity. In contrast, we highlight some of our recent work on hybrid polysaccharide (cellulose, pectin)—silica aerogels, where the mechanical reinforcement did not significantly increase thermal conductivity as a promising avenue for more robust silica-based hybrid aerogel materials.

International audience; Silica aerogels are excellent thermal insulators, but their brittle nature has prevented widespread application. To overcome these mechanical limitations, silica–biopolymer hybrids are a promising alternative. A one-pot process to monolithic, superinsulating pectin–silica hybrid aerogels is presented. Their structural and physical properties can be tuned by adjusting the gelation pH and pectin concentration. Hybrid aerogels made at pH 1.5 exhibit minimal dust release and vastly improved mechanical properties while remaining excellent thermal insulators. The change in the mechanical properties is directly linked to the observed “neck-free” nanoscale network structure with thicker struts. Such a design is superior to “neck-limited”, classical inorganic aerogels. This new class of materials opens up new perspectives for novel silica–biopolymer nanocomposite aerogels.

The wetting behavior of nanofibrillated cellulose (NFC) was drastically changed from hydrophilic to superhydrophobic, achieving limited contact angle hysteresis. Remarkably, superhydrophobicity was attained for a variety of morphologies, namely dense and porous films, foams and powders, thus exploiting a wide spectrum of cellulose manifestations. The superhydrophobic behavior resulted from the combined action of hydrophobic polysiloxane nanofilaments, formed by controlled reaction of methyltrichlorosilane with water at the surface of NFC fibrils, and the NFC substrates surface morphology, established by various drying methods of the nanofibrils. In particular, the optimal conditions for polysiloxane nanofilaments growth, with identification of various regimes of coating versus nanofilaments growth, were identified. Depending on the morphology, we demonstrated that modified NFC materials can act multiple roles, such as superhydrophobic liquid-infused lubricating surfaces, filters for dodecane drops capture from a nebulized dodecane/water mixture, hydrocarbon absorption from an aqueous phase, with absorbance capacity as high as 50 gdodecane/gfoam, and beds to separate hydrocarbon/water mixture. As such, the versatile combination of two materials with nanoscale features (nanocellulose and nanofilaments), which provide multi-tier topography and unprecedented wetting characteristics, can serve for all those applications, in which liquid mixture behavior (e.g. water/hydrocarbon) needs to be controlled.

Our current understanding of silicate melt structure and volatile speciation initially was derived mostly from infrared absorption and Raman spectroscopic observation. This is, for example, the case for the importance of topological changes during densification up to ∼15 GPa, the increase in coordination at higher pressures, and perhaps most strikingly, the speciation of volatiles in magmatic glasses and liquids. The picture that emerged from vibrational spectroscopy was later confirmed, and sometimes refined, by other techniques, but infrared and Raman spectroscopy remain two of the most informative and easily implemented analytical windows into the structure and volatile speciation of magmatic liquids, including in situ at high pressure and temperature.

The properties of silica aerogels and the ability to prepare them by ambient pressure drying hinge on their chemical surface modification. Until now quantitative analysis of the surface chemistry has not been possible by state of theart analytical methods. Here we determine the surface chemistry of six archetypal ambient pressure dried hydrophobic silica aerogels and open porous foams with quantitative 1H 13C and 29Si and 1H 29Si heteronuclear solid state NMR spectroscopy. The quality of the external calibration the validation by elemental analysis and the consistency among the 1H 13C and 29Si MAS NMR data enable us to robustly quantify the surface chemistry of these classical silica materials. Four aerogels were derived from tetraethoxysilane (TEOS) polyethoxydisiloxane (PEDS) or waterglass precursors and hydrophobized with trimethylsilyl (TMS) groups through immersion in hexamethyldisilazane (HMDZ) in heptane trimethylchlorosilane (TMCS) in heptane or hexamethyldisiloxane (HMDSO) in ethanol. The resulting aerogels display remarkably similar chemistries despite their very different precursors (alkoxides waterglass) hydrophobization agents (HMDZ TMCS HMDSO) and gelation and hydrophobization solvents (water ethanol heptane). The TMS content is nearly the same (22 27 wt ) the ethoxy content is low (

A fast and simple, one-step synthesis for the preparation of silica aerogel powders is reported. A waterglass based sol was prepared without prior ion-exchange and stirred with an immiscible organic phase (heptane) that contains the hydrophobization agent (hexamethyldisilazane). The addition of nitric acid triggers gelation and subsequently the hydrophobization of this hydrogel, which causes the gel particles to transfer from the aqueous into the organic phase, whilst the sodium and nitrate ions are retained in the aqueous phase. The resulting organogel slurry is then converted into a silica aerogel powder by means of ambient pressure drying. The addition of phase transfer agents, ethanol and isopropanol in particular, strongly influences the final silica aerogel properties, including tap density, hydrophobicity, particle size distribution, surface chemistry (solid-state NMR), and microstructure (TEM, SEM, nitrogen sorption). The addition of intermediate amounts of phase transfer agent strongly improves the aerogel properties, but these positive effects disappear when larger quantities are added. Under optimal conditions, silica aerogel powders with high mesoporosity, surface areas above 800 m2/g, tap densities as low as 0.083 g/cm3, and thermal conductivities below 20 mW m−1 K−1 can be produced in a one-step process within just over two hours. The direct use of waterglass as an inexpensive silica precursor provides a great opportunity to reduce the production cost of silica aerogel powders for thermal insulation applications.

The structures of high-pressure magmatic liquids have often been inferred from spectroscopic studies on quenched and decompressed glasses. However, it has not been completely verified whether the structures of quenched and decompressed glasses are representative of the structure of their corresponding liquids at the glass transition temperature and synthesis pressure. Here, we provide quantitative evidence for the retention of pressure-induced configurational changes upon isobaric quench and isothermal decompres-sion for synthesis pressures up to 3.5 GPa. We use the degree of densification and elastic compressibility of permanently densified glasses, together with thermo-elastic data from the literature, to calculate the density of the melt at the glass transition temperature and synthesis pressure. The derived densities agree with those derived directly from the thermal equations of state of the melts. This observation indicates that, at least up to 3.5 GPa, the densified structure of the melt is preserved in the glass upon quenching and decompression; this validates past and future structural studies of high-pressure melts based on studies of quenched and decompressed glasses.Keywords: Compressibility, silicate melts, relaxation, rhyolite, phonolite, basalt

The hydroxyl speciation of hydrous, metaluminous potassium and calcium aluminosilicate glasses was investigated by 27 Al– 1 H cross polarization and quantitative 1 H MAS NMR spectroscopy. Al-OH is present in both the potassium and the calcium aluminosilicate glasses and its 1 H NMR partial spectrum was derived from the 27 Al– 1 H cross polarization data. For the calcium aluminosilicate glasses, the abundance of Al-OH could not be determined because of the low spectral resolution. For the potassium aluminosilicate glasses, the fraction of Al-OH was quantified by fitting its partial spectrum to the quantitative 1 H NMR spectra. The degree of aluminum avoidance and the relative tendency for Si–O–Si, Si–O–Al and Al–O–Al bonds to hydrolyze were derived from the measured species abundances. Compared to the sodium, lithium and calcium systems, potassium aluminosilicate glasses display a much stronger degree of aluminum avoidance and a stronger tendency for the Al–O–Al linkages to hydrolyze. Combining our results with those for sodium aluminosilicate glasses (Malfait and Xue, 2010a), we predict that the hydroxyl groups in rhyolitic and phonolitic magmas are predominantly present as Si-OH (84–89% and 68–78%, respectively), but with a significant fraction of Al-OH (11–16% and 22–32%, respectively). For both rhyolitic and phonolitic melts, the AlOH/(AlOH + SiOH) ratio is likely smaller than the Al/(Al + Si) ratio for the lower end of the natural temperature range but may approach the Al/(Al + Si) ratio at higher temperatures.

Water is dissolved in silicate glasses and melts as hydroxyl groups and molecular water, with mostly hydroxyl groups at low water contents and mostly molecular water at high water contents. However, we recently predicted that water will be dissociated nearly completely in potassium aluminosilicate glasses with more alumina than silica because of the strong aluminum avoidance and the strong tendency for Al-O-Al linkages to hydrolyze in such glasses. In the present study, I test this prediction on hydrous K 2 Al 2 SiO 6 glasses: the Raman and infrared absorption spectra show that water is indeed predominantly present as hydroxyl groups, even for glasses with more than 7 wt% water. This observation validates the previously proposed speciation reactions, demonstrates that variations in water speciation are related to the nature of the cations to which the hydroxyl groups are bonded, and indicates that the classical picture of water dissolution, with predominantly molecular water at high water contents, may not apply near compositional extremes.

Hierarchically organized, porous materials exhibit unique combinations of physical and chemical properties depending on their pore sizes, pore structure and surface chemistry. Extraction and drying methods as well as post synthetic thermal treatments influence the characteristics of the resulting porous network and thus the achievable properties. Here we present a comprehensive investigation of the effects of drying conditions and post synthesis treatments on surface chemistry, pore structure and resulting mechanical properties of hierarchically structured silica monoliths comprising pores on three hierarchy levels (micro-, meso- and macropores). Samples were either dried supercritically (SCD) with carbon dioxide or at ambient pressure (APD) after surface silylation. In addition, the impact of a post synthetic heat treatment at two different temperatures (300 °C and 500 °C) is investigated. The focus of the study is on chemical and structural changes in/at the (meso-)pore walls, including the presence of micropores and the influence of organic components on the macroscopic properties. We discuss the implications of these modifications on mechanical properties, such as their deformation behavior during fluid adsorption related to their respective bulk and skeletal Young's moduli. Scanning electron microscopy, nitrogen adsorption/desorption measurements, simultaneous thermal analysis, solid-state NMR spectroscopy, small-angle X-ray scattering, sound velocity measurements and nitrogen adsorption/desorption with in-situ dilatometry were performed on each sample. This set of data illustrates the significant impact of different fabrication steps such as drying or calcination on material properties.

Recent O1s XPS studies suggest that significant free oxide (O2– or K–O–K) is present in potassium silicate glasses, in contrast with what was concluded from 29Si and 17O solid-state NMR data. An alternative peak assignment of the Qn peaks in the 29Si NMR spectra was proposed to bring the 29Si NMR data in line with the O1s data, but this reassignment (i) is not supported by any evidence other than the resulting agreement between the NMR and XPS data, (ii) is at odds with the spectral properties of the bands (peak position and width), (iii) ignores the strong evidence for the original peak assignment, and (iv) results in highly implausible equilibrium constants for the Qn speciation reactions. More likely causes for the apparent discrepancy between the XPS and NMR data are the incorrect estimation of the precision of the bridging oxygen content from the O1s XPS data, the systematic overestimation of the bridging oxygen content from the O1s XPS data, and (or) the incorrect estimation of the accuracy of the compositional analysis, which was based on the precision rather than the accuracy of the electron microprobe analysis. Thus, the available evidence strongly suggests that the original assignment of the 29Si NMR spectra is correct. Neither the 29Si NMR nor the O1s XPS data support the presence of significant amounts of free oxide in potassium silicate glasses with K2O/SiO2 ≪ 2.

article Carbon dioxide is the second most abundant magmatic volatile and strongly affects the chemical and physical properties of melts. However, the volumetric properties of CO2-bearing silicate melts and glasses are still poorly constrained.Inthisstudy,the density,acousticvelocitiesandelasticpropertiesofCO2-bearingbasaltic,phonolitic and rhyolitic glasses have been determined by the sink/float method and Brillouin scattering spectroscopy to constrain the effect of magma composition on the partial molar volume and compressibility of dissolved CO2. The glasseswere synthesized atelevatedpressuretoachieve highCO2contents, up to 3.9 wt.%,and subsequently annealed at room pressure to relax the pressure-induced densification. The relaxation times indicate that CO2 lowers the viscosity of basaltic melts, while that of rhyolitic and phonolitic melts remains unchanged. The partial molar volume of CO2 depends on the silicate composition with VCO2 = 26.6 ± 1.8, 22.1 ± 0.6 and 25.4 ± 0.9 cm 3 /mol, in basaltic, phonolitic and rhyolitic glasses, respectively, but is not a simple function of the CO2/ CO3 2− speciation. In addition, our data indicate a strong compositionally dependent partial molar adiabatic com

Large area seals were prepared between a metal foil frame (Fe-Ni alloy with 48 wt% Ni) and a 901 × 814 mm2 glass pane through the simultaneous application of activated liquid tin solder anodic bonding and soft soldering. An experimental facility including a liquid solder injector was built. Prototype seals were produced with tin solder alloys with variable Al contents and the hermiticity and interface integrity was determined. Solder alloys with an Al content of 112.5 ppm resulted in the strongest adhesion forces, broadly consistent with a previous study at the laboratory scale. The resulting prototypes consist of a bonded area of ∼450 cm2 along the perimeter of a 0.73 m2 glass pane and display consistently strong bonds for sections over a meter in length, demonstrating that activated liquid solder anodic bonding is not restricted to small-area applications.

Field observations and solubility experiments show evidence for the efficient mobilization of nominally insoluble HFSE (i.e., Ti, Zr, Nb and Hf) by high pressure fluids, probably via complexation with polymerized alkali–silica dissolved species and halogens (F and Cl). Here we investigate the complexation of Zr in subduction-related fluids (aqueous fluids and hydrous haplogranite melts) up to 800 °C and 2.4 GPa using X-ray absorption spectroscopy (XANES and EXAFS) in a hydrothermal diamond anvil cell and provide evidence for the formation of Zr–O–Si/Na polymeric species in alkali-(alumino)silicate fluids at high pressure. Zr4+ speciation in dilute fluids (2.5 wt% HCl) is dominated by 8-fold-coordinated [Zr(H2O)8]4+ hydrated complexes at room conditions and no evidence for extensive Zr–Cl complexation in the fluid was found up to 420 °C, as confirmed by ab initio XANES calculations of various ZrO8−xClx clusters. The addition of Na and Si dissolved species (from 35 to 60 wt% dissolved Na2Si2O5, NS2) into the fluid favors the formation of alkali-zirconosilicate clusters Zr–O–Si/Na similar to those found in vlasovite (Na2ZrSi4O11), with Zr4+ in octahedral coordination with oxygen (Zr–O distance = 2.09 ± 0.04 A) and ∼6 Si (Na) second neighbors (Zr–Si/Na distance = 3.66 ± 0.06 A). This coordination environment also dominates Zr speciation in F-free and F-bearing NS2 and haplogranite glasses and high pressure hydrous haplogranite melts (15.5–33 wt% dissolved H2O) in the investigated pressure–temperature range. The XAS analyses, assisted by ab initio XANES calculations, are not conclusive concerning the extent of Zr–F complexation in hydrous granitic melts. Alkali-zirconosilicate Zr–O–Si/Na clusters such as those identified in this study may explain the enhanced solubility of zircon ZrSiO4 (and other HFSE-bearing minerals) in alkali-aluminosilicate-bearing aqueous fluids produced by dehydration and melting of the slab and provide a favorable mechanism for the mobilization of HFSE in subduction zones. Fluid–rock interactions and/or P/T variations as fluids migrate through the mantle wedge could affect the stability of these complexes, triggering the precipitation of HFSE-bearing accessory phases that are eventually recycled into the mantle, contributing to the dispersion of HFSE. These processes provide a possible explanation for the characteristic HFSE depletion recorded in arc magmas.

Understanding magmatic processes and their evolution in the Earthʼs interior requires a better knowledge of silicate melts and their physical properties. Among them, density is one of the most important to constrain the residence or ascent time of magma in the upper mantle and crust. However, the volumetric properties of volatile-bearing and highly polymerized silicate melts are still poorly constrained due to scarce experimental data. In this study, the density of dry and hydrous (4.35 wt% H2O) phonolitic melt was measured in situ using the X-ray absorption method in a Paris–Edinburgh press at 0.73–3.1 GPa and 1484–1855 K. Calculated melt densities range from 2.49 ± 0.02 to 2.66 ± 0.03 g / cm 3 and from 2.31 ± 0.02 to 2.52 ± 0.02 g / cm 3 for the dry and hydrous compositions at depths of 30 to 100 km. The results are used to calibrate the equation of state (EoS) of phonolitic liquids for crustal and upper mantle conditions and to derive the partial molar volume of water: a least-squares fit of the P – T – ρ data to a third-order Birch–Murnaghan EoS yields: V 0 = 28.10 − 0.74 + 0.10 cm 3 / mol , K T = 14.6 − 3.0 + 3.2 GPa , K ′ = 8.9 − 2.6 + 3.3 and α = 47 − 30 + 28 × 10 − 6 / K for the dry melts and V 0 = 20.6 − 0.8 + 7.5 cm 3 / mol , K T = 4.6 − 3.0 + 2.3 GPa , K ′ = 5.5 − 0.5 + 6.1 and α = 135 − 115 + 114 × 10 − 6 / K for the hydrous component at 1673 K. Combined with literature data, our EoS for water indicates that V ¯ H 2 O does not depend strongly on the silicate liquid composition at the investigated conditions. Crystal settling velocities in phonolitic liquids were calculated from the EoS to constrain the time scales of crystal fractionation in magma chambers. The high compressibility of phonolitic melts results in a small density contrast between nepheline and sanidine crystals and melt ( Δ ρ neph - phon = 0.13 – 0.27 g / cm 3 and Δ ρ san - phon = 0.05 – 0.21 g / cm 3 ) with corresponding settling times of about 380 and 510 yr/km, respectively, for crystal sizes of 2 cm. Because of their higher density, similar-sized magnetite and augite only require about 31 and 100 yr/km, respectively. The observed phenocryst populations in phonolitic magmas indicate that the residence time was sufficiently long to fractionate augite and magnetite, but not sanidine and nepheline. Thus, our density data, combined with the phenocryst populations of the erupted lavas point to a residence time in the crust between a few tens to hundreds of years, consistent with estimates from U–Th–Ra isotope compositions.

The convection or settling of matter in the deep Earth's interior is mostly constrained by density variations between the different reservoirs. Knowledge of the density contrast between solid and molten silicates is thus of prime importance to understand and model the dynamic behavior of the past and present Earth. SiO2 is the main constituent of Earth's mantle and is the reference model system for the behavior of silicate melts at high pressure. Here, we apply our recently developed x-ray absorption technique to the density of SiO2 glass up to 110 GPa, doubling the pressure range for such measurements. Our density data validate recent molecular dynamics simulations and are in good agreement with previous experimental studies conducted at lower pressure. Silica glass rapidly densifies up to 40 GPa, but the density trend then flattens to become asymptotic to the density of SiO2 minerals above 60 GPa. The density data present two discontinuities at similar to 17 and similar to 60 GPa that can be related to a silicon coordination increase from 4 to a mixed 5/6 coordination and from 5/6 to sixfold, respectively. SiO2 glass becomes denser than MgSiO3 glass at similar to 40 GPa, and its density becomes identical to that of MgSiO3 glass above 80 GPa. Our results on SiO2 glass may suggest that a variation of SiO2 content in a basaltic or pyrolitic melt with pressure has at most a minor effect on the final melt density, and iron partitioning between the melts and residual solids is the predominant factor that controls melt buoyancy in the lowermost mantle.

The coordination state of the network formers Si and Al is one of the primary parameters describing the structure of silicate glasses and melts. In this experimental study, we use 27Al MAS NMR spectroscopy to investigate the effect of temperature, pressure and composition on the coordination of Al in dry and hydrous rhyolite and andesite glasses, quenched from pressures of up to 3.5 GPa. The spectra were collected at a high magnetic field of 20 Tesla to increase spectral resolution and allow for a direct quantification of the different Al coordinations. The disorder around [4]Al increases with increasing fictive temperature and pressure and with decreasing water content or peralkalinity. Al is predominantly (>98%) in fourfold coordination in all investigated samples. Nevertheless, systematic trends in Al coordination have been observed as a function of pressure, composition and water content. For the investigated pressure range, the proportion of [5]Al increases with increasing pressure, but decreases with increasing water content and proximity to the metaluminous join for rhyolite glasses. Within analytical uncertainty, the amount of [5]Al is independent of fictive temperature. The addition of water to andesite glasses does not decrease the amount of [5]Al, in contrast to the rhyolite glasses. Based on the glass data, we conclude that the majority of Al and Si will be present in fourfold coordination in metaluminous dry and hydrous rhyolite magmas at the temperature and pressure conditions relevant for the crust and the subducting slab (up to 3.5 GPa). However, consistent with previous predictions from model systems, more higher-coordinated Al may be present in andesite and peralkaline or peraluminous rhyolite melts, although the exact concentrations cannot be predicted accurately from the available data. Compared to more depolymerized melts, rhyolite melts can accommodate a higher degree of densification without a significant increase in Al coordination.

The combined results of 27Al–1H and 1H–29Si–1H cross polarization NMR experiments for hydrous glasses (containing 0.5–2 wt% water) along the SiO2–NaAlSiO4 join confirm that the dissolution mechanism of water in aluminosilicate glasses is fundamentally the same as for Al-free systems, i.e. the dissolved water ruptures oxygen bridges and creates Si–OH and Al–OH groups, in addition to forming molecular water (H2Omol). The fraction of Al–OH increases non-linearly as the Al content increases with up to half of the OH groups as Al–OH for compositions close to NaAlSiO4. The relative abundances of the different species are controlled by the degree of Al-avoidance and the relative tendency of hydrolysis of the different types of oxygen bridges, Si–O–Si, Si–O–Al and Al–O–Al. A set of homogeneous reactions is derived to model the measured Al–OH/Si–OH speciation, and the obtained equilibrium constants are in agreement with literature data on the degree of Al-avoidance. With these equilibrium constants, the abundance of the different oxygen species, i.e. Si–O–Si, Si–O–Al, Al–O–Al, Si–OH, Al–OH and H2Omol, can be predicted for the entire range of water and Al contents.

The Component-Resolved methodology was applied to (1)H spin-echo and (27)Al-(1)H cross polarization (CP) MAS NMR data of aluminosilicate glasses. The method was able to resolve two components with different T2 relaxation rates, hydroxyl groups (OH) and molecular water (H(2)O(mol)), from the spin-echo data and to determine partial spectra and the relative abundances of OH and H(2)O(mol). The algorithm resolved two to three components with different (27)Al-(1)H CP dynamics from the (27)Al-(1)H cross polarization data; the obtained partial NMR spectra for Al-OH are in excellent agreement with those obtained previously from the difference spectra between spectra with various contact times and confirm previous quantitative results and models for the Al-OH, Si-OH and H(2)O(mol) speciation (Malfait and Xue, 2010).

The position of the infrared absorption band near 4500 cm−1 shifts from 4520 to 4440 cm−1 as the Al content increases along the SiO2-NaAlSiO2 join and closely follows the sum of the positions of the Raman bands near 900 and 3600 cm−1. This confirms the idea that the 4500 cm−1 band is a combination band of the fundamental (Si,Al)-OH vibration near 900 cm−1 and the fundamental O-H stretching vibration near 3600 cm−1. As a consequence, the 4500 cm−1 band should not be used to quantify the water speciation for glass compositions for which significant amounts of free hydroxyls are expected as these do not contribute to the band’s intensity.

The silicate speciation forms an important aspect of the structure of silicate melts, a subject of interest to both the earth- and materials science communities. In this study, the Qn speciation of binary cesium silicate glasses was studied by Raman spectroscopy. A method to extract the equilibrium constant from a set of Raman spectra is presented, and the least-squares optimization algorithm is given (in Supporting Information). Log(K), the equilibrium constant of the speciation reaction, 2Q3 = Q4 + Q2, equals −2.72 ± 0.11 at the glass transition. This extends the previously established correlation between log(K) and the inverse of the ionic radius of the network modifier to cesium. Copyright © 2009 John Wiley & Sons, Ltd.

A 29 Si NMR spectrum with high signal to noise ratio was collected from a well-characterized, isotopically-enriched SiO 2 glass with a single scan after full relaxation of the magnetization. From the spectrum, the average Si–O–Si bond angle was estimated at 150° with a minimum fwhm of the bond angle distribution of 16°. The 29 Si spin-lattice relaxation times were measured by saturation recovery and differential T 1 relaxation was observed for the various Si environments.

In situ, high-temperature Raman spectroscopy was used to study the Q n speciation in binary Na-silicate glasses and melts. Over 300 Raman spectra in the compositional range from 25 to 40 mol% Na2O were collected at room and high temperatures between 800 and 1200 K. Quantitative information on the relative abundances of species in melts was obtained from the Raman spectra through a quantification procedure that does not require any a priori assumptions about the line shapes or external calibration of the Raman scattering efficiencies for the various Q n species. The Δ H ° associated with the speciation reaction 2 Q 3 = Q 4 + Q 2 was found to be 20.3 ± 7.9 kJ/mol. For a given temperature, the speciation is more disordered in sodium than in potassium silicate melts. Because of the smaller temperature dependence of the speciation in the sodium silicate system, the difference in the speciation for the sodium and potassium silicate system decreases with increasing temperature. In addition to the speciation data, the partial Raman spectra for the different species were obtained. The experimentally observed variation of the partial Raman spectra with temperature, and, to a minor extent, with composition, should stimulate future theoretical studies on the vibrational properties of silicate glasses and melts.

The use of a Carr–Purcell–Meiboom–Gill (CPMG) echotrain to increase the 29 Si NMR sensitivity in glasses was investigated. The echo intensity decay follows a stretched exponential behavior M( t ) = M 0 exp[−( t / t 2) β ] with values for the exponent β in the range of 0.41–0.65. The signal to noise in the spectra can be increased by a factor of up to 4 by taking the weighted sum of the spectra obtained from the individual echoes. However, differential T2 relaxation for the different Q n species is observed, with a shorter relaxation time for Q 4 than Q 3 . Thus, summing of the echoes leads to distorted spectral intensities and quantitative information can no longer be obtained from the spectra. To circumvent the problem with differential T2 relaxation, an alternative approach is developed in which the spectral intensity for each chemical shift value is determined from the stretched exponential fit to its echo decay. With this approach, the sensitivity can be increased by a factor of up to 2.4, while quantitative information can still be obtained from the spectra. The increased sensitivity permitted the detection of five-coordinated silicon in a potassium silicate glass with natural 29 Si abundance at ambient pressure.

Strong glass/solder/metal seals were prepared between float glass, tin solder and Fe-Ni alloys by the Activated Liquid Tin Solder Anodic Bonding (ALTSAB) process that combines classical anodic bonding with a liquid solder to ensure a near perfect contact between the bonding surfaces. The optimization of the Al content of the solder enables the production of glass/solder/metal joints without pre-treatment of the metal or glass surfaces. Strong glass/solder bonds are formed by anodic bonding across the oxide/metal interface and strong solder/metal bonds are formed simultaneously by soft soldering. The combined process consists of two very different processes and the optimal solder composition represents the middle ground between the requirements for both interfaces. The glass/solder bond strength increases with increasing Al content at the expense of the solder/metal bond strength: solders with a very low Al content of 75 ppm constitute the best compromise and result in the strongest glass/solder/metal joints. The optimal solder composition was used to anodically bond Dilaton Fe-48 wt%Ni frames to the edge of 500 × 500 mm2 float glass panes for vacuum glazing applications.

The structure of 21 binary potassium, rubidium and cesium silicate glasses (in the range 15–50 mol% alkali oxide) was analyzed by 29Si single quantum and double quantum MAS NMR spectroscopy. Their glass transition temperatures (Tg) were measured by calorimetry. The chemical shifts and the relative abundance of Qn species correlate with the cationic field strength (Z/r) of the network modifier. A correlation is observed between Tg and the inverse of the entropy of mixing of the different Qn species, which is explained in the framework of the Adam–Gibbs relaxation theory. At high alkali content, up to 44% of the SiO4 tetrahedra are part of three-membered rings. At a given alkali content, the abundance of these rings increases with increasing cation size. The abundance of three-membered rings in K-silicate melts correlates with a temperature and a non-linear composition dependence of the heat capacity. It is also a possible cause for the anomalous volumetric behavior of potassium silicate glasses.

In situ, high-temperature Raman spectroscopy was used to study the Q n speciation in binary potassium silicate melts. Over 300 Raman spectra in the compositional range from 20 to 38 mol% K 2 O were collected at temperatures between 800 and 1200 K. Quantitative information on the relative abundances of species in melts was obtained from the Raman spectra through a quantification procedure that does not require any a priori assumptions about the line shapes or external calibration of the Raman scattering efficiencies for the various Q n species. The Δ H 0 associated with the speciation reaction 2 Q 3 = Q 4 + Q 2 was found to be 33.1 ± 7.3 kJ/mol.

A mathematical approach was developed to interpret Raman spectra of binary silicate glasses and melts without the necessity of external calibration, e.g., from NMR spectroscopy. The developed approach is based on Principal Component Analysis (PCA), linear combinations of partial Raman spectra and a linear optimization technique. In order to apply and to test this approach, we developed an experimental method to collect a large number of Raman spectra efficiently. We applied the quantification and the experimental approaches to investigate potassium silicate glasses with compositions from 17.4 to 38 mol% K 2 O. The equilibrium constant for the reaction 2 Q 3 ⇄ Q 2 + Q 4 was found log K 3 = −2.37 ± 0.07, in excellent agreement with NMR studies for the same glasses.

Contributions to Mineralogy and Petrology, 150 (6), ISSN:0010-7999, ISSN:1432-0967

International audience; One key for understanding the stratification in the deep mantle lies in the determination of the density and structure of matter at high pressures, as well as the density contrast between solid and liquid silicate phases. Indeed, the density contrast is the main control on the entrainment or settlement of matter and is of fundamental importance for understanding the past and present dynamic behavior of the deepest part of the Earth's mantle. Here, we adapted the X-ray absorption method to the small dimensions of the diamond anvil cell, enabling density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up to 127 GPa are considerably higher than those previously derived from Brillouin spectroscopy but validate recent ab initio molecular dynamics simulations. A fourth-order Birch-Murnaghan equation of state reproduces our experimental data over the entire pressure regime of the mantle. At the core-mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 +/- 0.18 g/cm(3), which is only 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm(3), i.e., they are the same within the uncertainty. Taking into account the partitioning of iron into the melt, we conclude that melts are denser than the surrounding solid phases in the lowermost mantle and that melts will be trapped above the CMB

The partitioning of Zr between high P-T aqueous fluids and melts has been investigated in situ in the haplogranite-H2O and haplogranite-(F)-H2O systems to assess the mobilization of high field strength elements (HFSE) in magmatic-hydrothermal processes in subduction zones. The partition coefficients D f/mZr were determined from Zr concentrations measured in situ by synchrotron X-ray fluorescence (SXRF) in both aqueous fluids and F-free or F-bearing hydrous haplogranite melts equilibrated in diamond-anvil cells at 575 to 800 °C and 0.3 to 2.4 GPa. This experimental approach eliminates the need for internal or external calibrations of the SXRF signal and/or post-mortem analysis of the melt phase, hence decreasing the total uncertainties on D f/mZr below 16%. Above 0.6 GPa, Zr partitions favorably into the hydrous silicate melt in both F-free and F-bearing systems, with D f/mZr that range between 0.19 ± 0.02 and 0.38 ± 0.03. However, the relatively high D f/mZr values indicate that alkali-silica rich aqueous fluids generated by metamorphic devolatilization may contribute significantly to the recycling of HFSE in subduction zones. The efficient uptake of Zr (and likely other HFSE) by subduction zone fluids, regardless of their nature (aqueous fluid, hydrous melt, or supercritical fluid), supports the idea that the typical HFSE depletion recorded in arc magmas does not result from their incompatibility in water-rich slab-derived fluids but most probably originates from complex fluid-melt-rock interactions occurring at the slab interface and within the mantle wedge. At shallow crustal pressure conditions (800 °C and 0.3 GPa), Zr partitions reversely into the aqueous fluid in the presence of fluorine ( D f/mZr = 1.40 ± 0.10) as observed for Nb at similar conditions by Webster et al. (1989). The enrichment of the aqueous phase in HFSE (Zr, Nb) at shallow crustal conditions is likely related to the enhanced peralkalinity of low pressure, F-bearing aqueous fluid with temperature, that provides the favorable conditions for their mobilization via the formation of HFSE-O-Si/Na clusters. This mechanism may control the enrichment in HFSE (and plausibly other rare metals such as REE) in early magmatic fluids exsolved from granitic melts, leading to the formation of HFSE-enriched aggregates in shallow magmatic-hydrothermal environments (e.g., Strange Lake and Thor Lake Nechalacho deposit, Canada; Galineiro complex, Spain).

The kinetics of aging processes in emulsions of undecane and dodecane stabilized by a surfactant is studied by dynamic light scattering (DLS) and fiber-optics dynamic light scattering (FODLS). It appears that whereas DLS requires extremely diluted clear samples (volume fraction typically 2×10−4) to follow the aging process, FODLS allows to monitor the aging in concentrated (volume fraction 0.2) and extremely turbid emulsions. Quantitative agreement between FODLS and DLS is however only obtained when the aging is followed by FODLS on moderately diluted (volume fraction 0.01) emulsions. For more concentrated emulsions quantitative results from FODLS measurements on undiluted emulsions can only be obtained if prior knowledge about the effect of particle interaction on the measured diffusion coefficient is available. The observed variation of the ripening rates with the alkane volume fraction is in agreement with the theoretical predictions.